Retroverted passage type muffler with outer conduit formed of sound absorbing material



. J. B. GAFFNEY RETROVERTED PASSAGE TYPE MUFFLER 2,640,557 WITH OUTERJune 2,1953

2 Sheets-Sheet 1 Filed Dec.

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Jossm B. Gnnuzv 2 Sheets-Sheet 2 J. B. GAFFNEY RETROVERTED PASSAGE TYPEMUFFLER WITH OUTER CONDUIT FORMED OF SOUND ABSORBING MATERIAL Filed Dec.13, 1950 June 2, 1953 A I "g INVENTOR. JOSEPH B. Gnrrnev Patented June2, 1953 UNITED STATES.

PATENT OFFICE WITH OUTER CONDUIT FORMED OF SOUND ABSORBING MATERIAL.

Joseph B. Gaflney, Hokendauqua, Pa., assignor to Fuller Company,Oatasauqua, Pan, 2:. corporation of Delaware Application December 13,1950, Serial N 0. 200,654

8 Claims. 1,

This invention relates to the silencing and attenuating of pulsations ina flowing gas streamsuch as that produced in the intake and exhaust ofair pumps, internal combustion engines, and

the like; and is particularly adaptable to exhaust silencers forpositive pressure blowers.

It is especially concerned with the simple and effective means forsilencing the exhaust noises of a pneumatic conveying system withoutsubstantially increasing the back pressure of the exhaust system. It isamong the further purposes to provide a silencer that is equallyeffective in any position and that may be located at any point in theexhaust system with respect to the blower.

It is well known that the flOWiIlg gas stream in an exhaust system of apositive pressure blower comprises a series of separate gas slugs, orvolumes of gas, at a relatively high pressure separated by volumes ofgas at a relatively low pressure, and it is believed that the noise fromsuch an exhaust system is produced by these high pressure slugs of gashitting the surrounding air as the slugs are exhausted to atmosphere. Toovercome a noise of this type the high pressure volumes and the lowpressure volumes in the exhaust system must be smoothed out, orattenuated, to mean pressure to provide a constant. pressure stream ofgas flowing from the exhaust system to the atmosphere.

I It has been the practice to attenuate the variable pressures in anexhaust stream of gas by providing silencers having various obstructionsand expansion chambers through which the gas must fiow. The theory isthat the obstructions to the flow will cause a damming up of the streamof gas and a resulting co-mingling of the separate volumes of gas toeven out to a uniform pressure, while the expansion chambers will allowthe high pressure volumes of gas to lose momentum and expand into thevolumes of lower pressure gas. The objection to silencers of this typeis the usual increase in back pressure of the gas stream incurred as thestream is forced to flow around th obstructions and into and out of thevarious expansion chambers through restricted openings. A furtherobjection to silencers of this type isthe lack of any provision for theabsorption of sound waves produced by the vibrations set up from theflowing gas stream striking the various elements of the silencer.

The present invention is, accordingly, directed to an apparatus forsilencing the noises in an exhaust system that are produced by thevariations in pressure, or pulsations, in the gas stream. The

apparatus includes novel means to-receive and attenuate the pulsationsto provide for a constant pressure in the gas stream flowing to theatmosphere, and to obtain a maximum efficiency in the attentuating ofthe pulsations without substantially-increasing the back pressure in theexhaust system.

In general, the new silencer comprises a substantially cylindricalhousing having an intake end and a discharge end. Anopen ended gas inletconduit is positioned in the housing intake end, and is extendedconcentrically a substantial distance into the housing. In the samemanner a gas outlet conduit of equal diameter is positioned in thehousing discharge end and extended concentri'cally a substantialdistance into the housing. An intermediate conduit, having one endclosed and one end open, is positioned concentrically around the gasinlet conduit inside the cylindrical housing-with the closed endopposite the inner open end of the gas inlet conduit and the open endpositioned adjacent the intake end of the cylindrical housing. Thediameter of the intermediate conduit is such that the annular, oreffective area, of this conduit for the flow of gas is substantiallyequal to the area of the gas inlet conduit. In a lik manner a secondintermediate conduit of the same design is positioned concentricallyaround the gas outlet conduit and the efiective area of thls conduit issubstantially equal to the area of the gas outlet conduit. An outerconduit, formed of a sound absorbing material, is positionedconcentrically and externally of the two intermediate'conduits and isextended substantially the length of the housing to serve as a means ofcommunication between the open ends of the two intermediate conduits.The effective area of the outer conduit for the flow of gas issubstantially equal to the effective area of either of the intermediateconduits,- and it is seen that at al1 times the cross sectional areas ofthe gas stream through any part of the silencer is substantially equal.

The exhaust gas enters the silencer through the gas inlet conduit whereit is discharged into the first intermediate conduit. Due to the closedend of the intermediate conduit being positioned opposite the inneropened end of the inlet conduit the flow of gas is forced to changedirection as it is discharged from the inlet conduit and flow throughthe space defined by the inside of the intermediate conduit and theoutside of the inlet conduit, which has the same area as the, inlet,conduit and therefore offers no obstruction 'to the flow of the gas.There is a co-mingling of the volumes of gas of different pressures dueto turbulence as the flow of gas is reversed in direction and a furtherco-mingling as the gas takes the form of an annular ring of the samearea, but of thinner cross section, as it flows through the intermediateconduit. There is a further attenuating of the gas pressures as thedirection of flow is changed from the intermediate conduit into theouter conduit. The gas now moves the length of the silencer and in doingso, the stream is in intimate contact with a relatively large surface ofsound absorbing material. The gas stream is now quite thin in radialdirection and is therefore less able to maintain any vibration in aradial direction, and any such vibration would be eliminated by theabsorbing material. Ihis outer conduit also prevents any sound waves setup inside the silencer from reaching the casing, thus avoiding anyvibration and resulting noise from this source. The gas stream isdischarged from the outer conduit into the second intermediate conduit,and from this conduit it passes into the outlet conduit through which itis discharged from the silencer in a smooth even pressure stream.

For a better understanding of the nature of the invention, referenceshould be had to the following detailed description taken in connectionwith the accompanying drawings in which:

Fig. l is a plan view of the apparatus with sec tions broken away forthe purpose of illustration;

Fig. 2 is a plan view in section along with center line of theapparatus;

Fig. 3 is a sectional view taken on line 3-3 of Fi 1;

Fig. 4 is a sectional view taken on line 4-4 of Fig. 1.

Referring to the drawings the silencer is disclosed in a verticalposition and will be described in such a. position for the purpose oforientation, l

but it is to be understood that although the apparatus is disclosed andusually installed in this position it will function equally eflicient inany position. The silencer will be seen to comprise the casing 5 whichis of generally cylindrical form, and which is formed by two chambers Gand I. Chambers 6 and I are fabricated as separate units to facilitatemanufacture, but are formed into a single unit by means of flanges 8 andsecured together by bolts I0. Chamber 6 will be described as the intakesection of the apparatus and chamber 1 will be described as thedischarge section. The casing 5 is closed at the discharge end by an endplate II secured to the casing by means of a flange and bolts 26.Positioned above the end plate II is a flange plate i2, of smallerdiameter, and plates II and 12 are spaced apart and held in position bya series of spacer plates I3 positioned 90 degrees apart. In a likemanner the intake end of casing 5 is closed by an end plate I 4 securedto the casing by m ans of a flange 25 and bolts 28. Positioned below theplate I 4 is a flange plate I5 of a smaller diameter than plate I4, andplates I4 and I5 are spaced apart and held in position by a series ofspacer plates I5 positioned 90 degrees apart. Plates I2 and I5 are usedas a means of attaching the silencer into an exhaust system.

Each end plate and flange plate is provided with aligned openingsthrough which is mounted an open ended conduit, the conduit terminatingat one end flush with the flange plate and passing through the openingin the end plate to extend concentrically a substantial distance intothe casing 5. The gas inlet conduit I7, secured to the end plate I4, isused as a means for conducting the gas stream into the casing 5; whilethe gas outlet conduit I8, secured to end plate II, is used as a meansfor conducting the gas stream from the inside of casing 5. The conduitI1 is provided at its discharge end with a series of inlet ports 30spaced around the circumference of conduit I1 and divided into equaldistance center lines along a portion of the length of the conduit. Thetotal combined area of the inlet ports is equal, or substantially equal,to the area of the conduit II. In a like manner conduit I8 is providedwith a series of inlet ports 3| at its discharge end positioned with thesame spacing as is provided for conduit IT.

A first intermediate conduit I9 extends concentrically into the casing 5externally of the gas inlet conduit I1, and is attached to the end plateM by means of bars 2|. The intermediate conduit I 9 is open at one endand closed at the other end by a conical plate 22 positioned oppositethe inner open end of the gas inlet conduit [1. The annular, oreffective cross-sectional area, of the first intermediate conduit isdefined by the space between the outside of the gas inlet conduit I! andthe inside of the intermediate conduit I9, and this effectivecross-sectional area is equal, or substantially equal, to the insidecross-sectional area of the gas inlet conduit IT. In a like manner asecond intermediate conduit 20 extends concentrically into the casing 5externally of the gas outlet conduit I8 and has an effectivecross-sectional area equal, or substantially equal, to the insidecross-sectional area of the gas outlet conduit. The second intermediateconduit 26, attached to the end plate I I by means of bars 23, is openat one end and closed at the other end by a partially conical plate 24,the closed end being positioned opposite the inner open end of the gasoutlet conduit I8. The conduit I9 is provided at its discharge end witha, series of ports 32 spaced regularly around the circumference of theconduit and divided into equal distant center lines along a portion ofthe length of the conduit, the total combined cross sectional area ofthe inlet ports are equal, or substantially equal, to thecross-sectional area of the conduit I9. In a like manner conduit 20 isprovided at its discharge end with a series of inlet ports 33 positionedwith the same spacing as is provided for conduit I 9.

An acoustic outer conduit is formed by two porous walls 2'! and 28spaced apart by a blanket of sound absorbing material 29, such as fiberglass. This outer conduit extends the entire length of easing 5 and hasan outer diameter slightly less than the inside diameter of the casing5. The acoustic outer conduit is comprised of two units, outer conduit35 positioned inside chamber 6 and outer conduit 36 positioned insidechamber I. The inside diameter of conduit 35 is of such dimension thatthe effective area, that is the area defined by the space between theoutside of conduit I9 and the inside Walls 28 of the conduit 35, isequal, or substantially equal, to the eifective area of the conduit l9.This dimension relationship also applies to the conduit 36 with respectto the conduit 20. As stated before, this apparatus is usually installedin a vertical position and may be outside of any weather shelter. In theevent that there is an installation without any shelter, there is aprobability that rain or other forms of moisture will enter theapparatus. To overcome this, a drain 34 has been provided atthe bottomof conduit 20 to permit any accumulated moisture entering the conduit [8to be removed;

In the. operation of the silencer, compressed gas, delivered: by ablower into the exhaust system, enters the silencer through the inletconduit il in: the form of a. gasstream comprised of a series ofseparate gas slugs, or volumes of gas, at arelatively high pressureseparated by volumes of gas at a. relatively low pressure. separateslugs of gas'move through the inlet conduit with: an inertiasufficiently high. to carry:

them rapidlypast the ports 30 spaced around the circumference of theinner end of the conduit I? and to' discharge them into the'closed endsection of the firs ntermediateconduit l9. stream, entering the closedend section of the first intermediate conduit, strikes a cushion of airpocketedv in the conical plate 22. This cushion of air is maintained inthe closed end section of the first intermediateconduit at all timesbecause of the conical shape of plate 22,. and acts as a sound absorberby preventing the separate slugs of gas from. striking the'plate 22 withfull force.

The gas stream, after striking the air cushion, is reversed in directionand starts: toward the open end of the first intermediate conduit [9,which by design has the same, or substantially the same, effective crosssectional area as that of the inlet conduit, and therefore offers noincreased resistance to theiflow of the gas stream. There is aturbulence in the gas stream as the direction of flow is reversed, andthis turbulence will cause a partial equalization of pressures. Thisequalization. is brought about by the comingling of the high pressurevolumes with the low pressure volumes wherein the high pressures will bereducediby expanding into the lower pressures, and: the low pressureswill be increased. This means that equalization of pressures isprevalent' throughout. the silencer wherever the direction of now of agas stream is reversed. The turbulence of. the gas stream is stillpresent as the gas moves toward the open end of the first intermediateconduit and past the ports 30 of the inlet conduit. This turbulence willcause some of the high pressure volumes, as well as the low pressurevolumes now at a higher pressure, to flow through the ports 30 andexpand into the low pressure volumes flowing past in the inlet conduit.

The gas stream, now in the form of a series of annular slugs, continuesthrough the first intermediate conduit to the open end of the conduitwhere its inertia carries it past the ports 32 into a chamber formed bythe closed end of the outer conduit 35. The gas stream strikes a cushionof air containedin the closed end of the outer conduit and isagainprevented from striking an element of the silencer with fullmomentum as its direction of how is reversed. A second turbulence iscreated by the reverse flow of the gas stream into the outer conduitresulting in a further co-mingling of the separate volumes and anequalizing of pressures in addition to a further equalized pressures Inflowing through. the outer conduit the gas stream is in intimatecontact. with a. relatively These- The gaslarge surface of soundabsorbing material; The

stream isnow quitethin radially'andthereforeless able to maintain anyvibration in a radial. direction, and any such vibration is eliminatedby the absorbing material; This sound absorbingmaterial is by designthick enough to absorb any additional. sound waves that may exist due tothe intermittent. pulsating'action of the blower impellers andby'thevibrations set up by the-turgas making up the gas stream, and abypassing or" a portion of the gas stream from. the second intermediateconduit through the ports 33 into theouterconduit, as describedfor othersections of the silencer. The gas stream flows through the conduit 29where it strikes the partial conical plate 24-, which'by design ofiers aminimum resistance'to the flow of. the gas as it changes direc tion toflow into the outlet conduit H3. The convex shape of the conical plate24 serves to facilitate the reversal of the annular how at this pointand the conversion of the annular ring of gas back into a single uniformcross sectional conduit. This is a desirable feature as the separatevolumes of gas are now at a uniform pressure and. have thecharacteristics of a constant pressurestrcam of gas and should beexhausted from the silencer through the outlet conduit IS with. aminimum amount of turbulence.

In the design of this silencer all crosssectional. areas of flow arekept equal, or substantially equal,.which results inthe velocity of thegas stream remaining constant and the only change taking place beingthat of. pressure equalization of the separate volumes of gas within thegas stream. This design of the silencer also furnishes a. means forcreating a concentric flow of gasthrough the apparatus whichprogressively becomes thinner in radial cross section, and thereforemore responsive. to. pressure equalization, until it reaches itsthinnest cross sectional area. where. it has its greatest areaexposeclto and. in intimate contact with, a sound absorbing material.

I claim:

1. A. silencer comprising a substantially cylindrical housing having anintake end and a. discharge end, an open ended gas inlet conduitpositioned in the housing intake end. and extending concentrically asubstantial distance therein, the inlet conduit having a'series of gasports positioned around. its circumference and spaced along a portion ofthe lengthof its inner end, an open ended gas outlet conduit positionedin the housing discharge end and extending concentrically a substantialdistance therein, the outlet conduit having a series of gas portspcsitioned around its circumference and spaced along a portion of thelength from its inner end, a first intermediate conduit having one endopened and one end closed positioned concentrically and externally alonga substantial. por-- tion of the" inlet conduit, the closed end of thefirst" intermediate conduit being positioned inwardly' from the innerend of the inlet conduit; theaopenzend of the firstiintermediate conduitbeing positioned inwardly from the intake end of the housing, the firstintermediate conduit having a series of gas ports positioned around itscircumference and spaced along a portion of the length from its openend, a second intermediate conduit having one end open and one endclosed positioned concentrically and externally along a substantialportion of the outlet conduit, the closed end of the second intermediateconduit being positioned inwardly from the inner end of the outletconduit, the opened end of the second intermediate conduit beingpositioned inwardly from the discharge end of the housing, the secondintermediate conduit having a series of gas ports positioned around itscircumference and spaced along a portion of the length from its openend, and an outer conduit formed of sound absorbing material positionedconcentrically about and spaced from the two intermediate conduits andextending substantially the length of the housing, the outer conduitforming an annular space about the two intermediate conduits whichprovides a means of communication between the open ends of the twointermediate conduits.

2. A silencer comprising a substantially cylindrical housing having anintake end and a discharge end, an open ended gas inlet conduitpositioned in the housing intake end and extending concentrically asubstantial distance therein, an open ended gas outlet conduitpositioned in the housing discharge end and extending concentrically asubstantial distance therein, the cross-sectional area of the gas inletconduit being substantially equal to the cross-sectional area of the gasoutlet conduit, a first intermediate conduit having one end open and oneend closed positioned concentrically and externally along a substantialportion of the inlet conduit, the effective cross-sectional area of thefirst intermediate conduit where it extends along the inlet conduitbeing substantially the same as the cross-sectional area of the inletconduit, the closed end of the first intermediate conduit beingpositioned inwardly from the inner end of the inlet conduit, a secondintermediate conduit having one end open and one end closed positionedconcentrically and externally along a substantial portion of the outletconduit, the effective cross-sectional area of the second intermediateconduit where it extends along the outlet conduit being substantiallythe same as the cross-sectional area of the outlet conduit, the closedend of the second intermediate conduit being positioned inwardly fromthe inner end of the outlet conduit, and an outer conduit positionedconcentrically about and spaced from the two intermediate conduits andextending substantially the length of the housing, the efiectivecross-sectional area of the outer conduit where it extends along theintermediate conduits being substantially the same as the effectivecross-sectional area of either of the two intermediate conduits, theouter conduit forming an annular space about the two intermediateconduits which provides a means of communication between the open endsof the two intermediate conduits.

3. A silencer comprising a substantially cylindrical housing having anintake end and a discharge end, an open ended gas inlet conduitpositioned in the housing intake end and extending concentrically asubstantial distance therein, the inlet conduit having a series of gasports positioned around its circumference and spaced along a portion ofvthe length thereof from its inner end, the combined cross-sectionalareas of the series of ports being substantially equal to thecross-sectional area of the gas inlet conduit, an open ended gas outletconduit positioned in the housing discharge end and extendingconcentrically a substantial distance therein, the outlet conduit havinga series of gas ports positioned around its circumference and spacedalong a portion of the length thereof from its inner end, the combinedcross-sectional areas of the series of ports of the outlet conduit beingsubstantially equal to the cross-sectional area of the gas outletconduit, a first intermediate conduit having one end open and one endclosed positioned concentrically and externally along a substantialportion of the inlet conduit, the closed end of the first intermediateconduit being positioned inwardly from the inner end of the inletconduit, the open end of the first intermediate conduit being positionedinwardly from the intake end of the housing, the first intermediateconduit having a. series or" gas port positioned around itscircumference and spaced along a portion of the length from its openend, the combined crosssectional areas of the series of ports of thefirst intermediate conduit being substantially equal to the enectivecross-sectional area of the first intermediate conduit where it extendalong the inlet conduit, a second intermediate conduit having one endopen and one end closed positioned concentrically and externally along asubstantial portion of the outlet conduit, the closed end of the secondintermediate conduit being positioned inwardly from the inner end of theoutlet conduit, the open end of the second intermediate conduit beingpositioned inwardly from the discharge end of the housing, the secondintermediate conduit having a series of gas ports positioned around itscircumference and spaced along a portion of the length from its openend, the combined cross-sectional areas of the series of ports of thesecond intermediate conduit being substantially equal to the effectivecross-sectional area of the second intermediate conduit where it extendsalong the outlet conduit, and an outer conduit formed of sound absorbingmaterial positioned concentrically about and spaced from the twointermediate conduits and extending substantially the length of thehousing, the outer conduit forming an annular space about the twointermediate conduits which provides a means of communication betweenthe open ends of the two intermediate conduits.

4. A silencer comprising a substantially cylindrical housing having aninlet end and a discharge end, an open ended gas inlet conduitpositioned in the housing intake end and extending concentricall asubstantial distance therein, the inlet conduit having a series of gasports positioned around its circumference and spaced along a portion ofthe length of its inner end, the combined cross-sectional areas of theseries of ports being substantially equal to the cross-sectional area ofthe gas inlet conduit, an open ended gas outlet conduit positioned inthe housing discharge end and extending concentrically a substantialdistance therein, the outlet conduit having a series of gas portspositioned around its circumference and spaced along a portion of thelength from its inner end, the combined crosssectional areas of theseries of ports of the gas outlet conduit being substantially equal tothe cross-sectional area of the gas outlet conduit, the cross-sectionalarea of the gas inlet conduit being substantially equal to thecross-sectional area of the gas outlet conduit, 2. first intermediateconduit having one and open and one end closed positioned concentricallyand externally about a substantial portion of the inlet conduit, theclosed end of the first intermediate conduit being positioned inwardlyfrom the inner end of the inlet conduit, the open end of the firstintermediate conduit being positioned inwardly from the intake end ofthe housing, the first intermediate conduit having a series of gas portspositioned around its circumference and spaced along a portion of thelength from its open end, the combined cross-sectional areas of theseries of ports of the first intermediate conduit being substan tiallyequal to the eiiective cross-sectional area of the first intermediateconduit, the effective cross-sectional area of the first intermediateconduit Where it extends along the inlet conduit being substantially thesame as the cross-sectional area of the inlet conduit, a secondintermediate conduit having one end open and one end closed positionedconcentrically and externally about a substantial portion of the outletconduit, the closed end of the second intermediate conduit beingpositioned inwardly from the inner end of the outlet conduit, the openend of the second intermediate conduit being positioned inwardly fromthe discharge end. of the housing, the second intermediate conduithaving a series of gas ports positioned around its circumference andspaced along a portion of the length from its open end, the combinedcross-sectional areas of the series of ports of the second intermediateconduit being substantially equal to the eifective cross-sectional areaof the second intermediate conduit, the effective cross-sectional areaof the second intermediate conduit where it extends along the outletconduit being substantially the same as the cross-sectional area of theoutlet conduit, and an outer conduit formed of sound absorbing materialpositioned concentrically about and spaced from the two intermediateconduits and extending substantially the length of the housing, theefiective area of the outer conduit where it extends along theintermediate conduits being substantially the same as the effective areaof either of the two intermediate conduits where they extend along theinlet and outlet conduits, the outer conduit forming an annular spaceabout the two intermediate conduits which provides a means ofcommunication between the open ends of the two intermediate conduits.

5. The silencer defined in claim 4 wherein the closed end of the firstintermediate conduit is a plate having a concave shape with respect tothe inner end of the inlet conduit, and the closed end of the secondintermediate conduit is a plate of convex shape with respect to theinner end of the outlet conduit.

6. The silencer defined in claim 4 wherein the closed end of the firstintermediate conduit is a plate having a concave conical shape withrespect to the inner end of the inlet conduit, and the closed end of thesecond intermediate conduit is a plate having a convex partially conicalshape with respect to the inner end of the outlet conduit.

7. The silencer defined in claim 6 wherein the second intermediateconduit is provided with means for removing accumulated condensate.

8. The silencer defined in claim 1 in which the gas ports in theintermediate conduits are positioned axially outwardly substantiallyfrom the inner end of the series of gas ports in the inlet and outletconduits, respectively.

JOSEPH B. GAF'FNEY.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,051,130 Lattime Jan. 21, 1913 1,057,485 Knollmann Apr. 1,1913 1,115,873 Spencer Nov. 3, 1914 1,553,264 Reasonover Sept. 8, 19251,772,589 Beamer Aug. 12, 1930 1,966,620 Flour July 17, 1934 2,455,965Wohlberg Dec. 14, 1948 FOREIGN PATENTS Number Country Date 461,065 GreatBritain Feb. 9, 1937 593,282 Great Britain Oct. 13, 1947

